The effect of voltage and metal-transfer mode on particulate fume size during the GMAW of plain carbon steel
Particulate-welding fumes can enter unciliated airways, or may even be absorbed through the skin, possibly to the detriment of the health of welders. The size and shape of the particulates will determine their ability to infiltrate the human body. Hence, the sensitivity of particulate-fume size to welding parameters such as arc voltage (20–36 V) and metal-transfer mode (dip, globular and spray) was assessed. Transmission electron microscopy (TEM) imaging was used for determining particulate-fume size and it was found to be an accurate, reproducible, and relatively simple technique. The results revealed a higher percentage of ultra-fine particulates (i.e. in <20 nm and>20–40 nm intervals) in ‘low-welding voltage’ fume plume compared with ‘high-welding voltage’ fume plume. Fundamentally, the fume plume created during dip metal-transfer at low-welding voltages (20–26 V) had much lower levels of particulate-fume concentration compared with spray metal-transfer at high-welding voltages (30- 36 V). TEM also revealed that for the range of welding voltages and metal transfer modes investigated, the particulates produced were predominantly less than 100 nm in diameter and spherical. Spherical particles (<100 >nm) have been reported elsewhere to reach the alveoli in rats and, hence, may be of relevance with respect to the health of welders. Slightly faceted crystalline particulates and fume-particle sizes of up to 800 nm in diameter were also observed with TEM. It should be noted that the agglomeration behaviour of these particulates in the fume plume is considered important but not entirely understood. The particle-size results suggest that the key to welder safety is to minimise cumulative exposure to particulate fume over their working life, irrespective of the welding parameters used. Innovative fumeextraction techniques, clean workshops, automated welding, and low-welding fume consumables should all form part of an integrated solution to help ensure the health and well being of welding personnel.